Crystal controlled oscillator circuit



Jan. 29, 1935.

Filed March 9, 1932 INVENTORS H. E. GOLDSTINE BY J. W. K

A'T 0R W Patented Jan. 29, 1935 UNITED STATES CRYSTAL CONTROLLED OSCILLATOR CIRCUIT 1 Hallan E. Goldstine and James W. Conklin, Rocky Point, N. Y., assignors to Radio .Corporation of America, a corporation of i DeIaw'are APDIiGationMarchB, 1932, Serial-No. 597,740- 3 Claims. 1(01. 250-36) Professor Cady has described in connection with Figure 3 of his United States Patent 1,472,583, an efiicient crystal controlled oscillator. This oscillator makes use of a crystal and a parallel tuned circuit in the grid circuit of an electron discharge device which is set into oscillation partly due to regenerative interelement feed back of the device, and partly due to regenerative inductive feed back by means of a tickler coil, to the parallel tuned input circuit.

However, due to the fact that the capacitive reactance of the crystal. holder at resonance is equal in magnitude to the resistance of the crystal, but 90 degrees away from or in quadrature therewith, it is apparent that even with the crystal controlling the voltages generated, the resonance curve of the oscillator as a whole is not as sharp as. it could be. Accordingly, to sharpen the resonance curve of the oscillator and cause controlling grid' voltages to" be applied to thegri'd at correct phase for only oscillation generation at the desired frequency, is the principal object of our present invention; To ,do soywe provide an arrangement whereby the reactance of the crystal holder is rendered ineffective for altering thephaseof voltagesapplied to the con.-

trol grid of the electron discharge device; Not only does this" arrangement sharpen the "fre- 'quency characteristic of the oscillating system as a whole, but, it will be found that even with relatively heavy loads on the crystal oscillator, the output need not be lowered to insure frequency stability as would be the case without our present invention.

Our present invention is described more fully with the aid of the accompanying drawing,

wherein, as illustrated diagrammatically in Figures 1, 2, 3 and 4, preferred embodiments and in wiring diagram form of our improved crystal controlled oscillating systems are shown.

Between the control grid 2 and cathode 4, shown in Figure 1 as of the A. C. heated type and in Figure 2 as of the indirectly heated type, although any other type may be used, there is shown an electromechanical vibrator or piezoelectric crystal controlling element 6. Also, be-

tween the grid 2 and filament 4 there is connect- 1 ed the parallel tuned circuit 8 comprising an inductance coil 10 shunted by a variable tuning condenser 12. Some intermediate point along the inductance or reactance 10 is connected through return lead 12 to the filament or ground. The upper end of the parallel tuned circuit 8 is connected to one electrode of piezo-electric crystal 6 and the other side of the parallel tuned circuit is connected through neutralizing cone denser 14 to another electrode of piezo-electric crystal 6. By variation of condenser 14 the capacity formed by the electrodes'of piezo-electric crystal 6 may be neutralized, .preferably completely, or to any desired extent-.

We prefer, however, that the circuit be made slightly degenerative, thereby neutralizing any extraneous capacities and over compensating-for any chanceof the circuit oscillating. Byhaving'a degenerative feedback, the output will not be lowered due to the degeneration because 'thelow series impedance of the crystal will causethe circuit to oscillate practically as strong at the fundamental crystal frequency.

Inductance feed back'froin the plate l6-is accomplished through tickler coil or feed back coil l8 -grounded for high frequency currents-at its potential supply end 20' through the action of blocking or' by-passingcondenser 22, electrostatic shielding 24 is provided between "the coils-18', lto prevent to any desiredrd'egree capacitive coupling therebetwe'en; Output'energ-y is derived t hrough blocking condenser... 26 through the leads indicated output .on: the drawing;

For establishing high ohmic value. a a

At resonance, {the capacitance. offthe crystal and its-associated electrodes has: a...v"alue maimpedance-e'qual to the. resistance Offth iresonator at the desired frequency. Consequently, it will be obvious that at the desired frequency the phase of voltages applied to the grid and plate will not be exactly that required for best operation at the natural frequency of the crystal. Accordingly, by adjustment of condenser 14 until the capacitive reactance of the crystal and its associated electrodes are eliminated or effectively neutralized or compensated, the circuit will oscillate at a frequency corresponding almost exactly with that frequency for which the I crystal is ground. In addition, as already pointed out, variations in load will produce no effective reaction back upon the crystal as a result of which relatively large stable outputs may be derived from the presentsystem.

As a further improvement, there may be provided in shunt with the grid leak resistor 28, a low impedance, connected across the grid 2-filament 4 circuit in the form of a resistance 30 in series with a by-passing condenser 32. Resistance 30 is of relatively low value, and, prevents the generation of spurious oscillations through a suitable bias on; control grid 2', resistor 28 is -providedi and-.Jis preferably of its by-passing effect. However, oscillations of desired frequency are built up in the parallel tuned circuit 8 by virtue of the lower impedance to the desired frequency offered by crystal 6, as a result of which in the output circuit of the system, only energy of desired frequency, namely that of the crystal, appears. This action is more fully described in the copending applications of C. W. Hansell and Harold O. Peterson, Serial #598,566 and 596,19'7, respectively, filed March 14, 1932 and March 2, 1932, respectively, wherein it has been shown also that the resistance'30, maybe replaced by a choke coil, or, merely by a cone denser of suitable value. 7, 7

In the arrangement shown in Figure 2, the parallel tuned circuit 8 has been replaced by an inductive reactance or coil 10 shunted'by two serially connected condensers 13,15. The

, trodes, a connection from one of said crystal electrodes to said grid, a connection from the other return lead 12 is connected to a point intermedie ate the condensers 13, 15 rather than to some intermediate point on the reactance or coil 10. The neutralizing 'condenser14 is connected in a similar fashion as that given in Figure 1 and in general the operation of both schemes are identical.

However, in the arrangement shown in Figure 2, neutralizing condenser 14 may be dispensed with, the neutralizing connection being made to some intermediate point on the grid tuning condenser. Further, if desired, condensers 13, 15 are made independently variable, rather than of the unicontrol variety.

In addition, in the arrangement shown'in Figure 2, a screen grid tube has been illustrated having a screen grid 40 suitably grounded for high frequency currents by the action of by-passing condenser 42. In this manner also, undesired interelement feed back is prevented as a result .of which tendencyitowards spurious or parasitic oscillation generation is still further prevented.

If desired, the neutralizing circuit may be inductively: coupled a to either,.the plate circuit: or grid circuit as shown diagrammatically in Figures 3 and 4. In Figure 3, desired neutralization is accomplished'by coupling coil 50 to the plate coil 18; and, in Figure 4 it is accomplished by couplingcoil 50170 the grid inductance coil 10. Having thus described our invention, what we claim is:

1.,.A constant frequency oscillator comprising a tube having an anode, a cathode,,anda grid,

a parallel tuned circuit having a-coil; and a condenser, a two electrode piezo-electric crystal, a connection from one terminal of said crystal to one end of said tuned circuit, a connection from the other terminal of said crystal to said grid, a connection from an intermediate point on said parallel tuned circuit to said cathode, a neutralizing condenser, a connection from one terminal of said neutralizing condenser to said grid, a connection from the other terminal of said neutralizing condenser to the other end of said tuned circuit, and a feedback coil connected between said anode and cathode and coupled to the coil of said tuned circuit.

2. A constant frequency oscillation generator comprising a tube having an anode, a cathode and a grid, a tuned circuit comprising an inductance coil and a condenser connected in parallel, a piezo electric crystal having two elecof said crystal electrodes to one terminal of said parallel tuned circuit, a connection from a point intermediate the ends of said coil to said cathode, a neutralizing condenser, a connection from one terminal of said neutralizing condenser to. said grid, a connection from the other terminal of saidneutralizing condenser to the other terminal of said parallel tuned circuit, and a feedback coil connected between said anode and cathode and coupled to the coil of said parallel tuned circuit. g

3. A constant frequency oscillation generator comprising a tube having an anode, a cathode, and a grid, an inductance coil, a pair of serially connected condensers connected in shunt to said inductance coil, said condensers and coil forming a parallel tuned circuit, a piezo-electric crystal having two electrodes, a connection from one of said crystal electrodes to said grid, a connectionfrom the other of said crystal electrodes to one terminal of said parallel tuned circuit, a connection from a point between said serially connected condensers to said cathode, a neutralizing condenser, a connection from one terminal of said neutralizing condenser to said grid, a connection from the other terminal of said neutralizing condenser to the other terminal of said parallel tuned circuit, and a feedback coil connected between said anode and cathode and coupled to the coil of said parallel tuned circuit.

HALLAN E. GOLDSTINE. JAMES W. CONKLIN. 

